I bought a phone I phone plus6 and she can’t remember the passcode to the Apple ID what do I do

Do you mean ther passcode to the phone? - the four or six digit number used to lock only that device. (If your Apple ID was locked you wouldn't be able to post here or indeed do anything with iCloud or Apple Music etc.)

The passcode is stored only on the phone, so it can't be retrieved. If you don't know it your only option is to erase the phone. Please see the page linked to at the top of this page.

the activation lock is not really on the iphone it's a

theft protection measure on apples servers

it needs to be removed

How to remove Activation Lock - Apple Support

if you don't know your appleID

Recover Your Apple ID - Apple

that does not help you then you need the assistance of apple

Additional Support - Activation Lock (apple.com) and or

Get Support (apple.com) , Genius Bar Reservation and Apple Support Options - Apple